The invention relates to a method for use in coil pipe operations and a device for carrying out the method, wherein a coil pipe is coiled up on a rotatable drum and is coiled off and up thereon by means of a feeding device adapted to feed the coil pipe off and onto the drum, well known under the term "injector", which is placed downstream in relation to the coil pipe drum, and which has a centric coil pipe passage defined between two opposing movable drive means exhibiting reversible directions of motion, and which attacks from either side on the coil pipe and, thus, displaces it in a direction towards the drum or away therefrom.
Coil pipes of this kind are subjected to several strains in the form of bending and straightening movements at each coil pipe operation or run. Upon uncoiling, a straightening movement of the coil pipe from the curved course thereof on the drum takes place at first, whereafter follows a bending of the coil pipe across a curved face, the so called "swan neck". Also the coil pipe is subjected to the same straightening and bending movements when it is in the course of being coiled up on the drum.
As distinct from a conventional drill string, a coil pipe is without joints and is very advantageous in this respect, but said bending and straightening movements lead to metal fatigue, and the coil pipe must be replaced after a certain number of runs or trips down into the well.
On floating platforms, the injector and the swan neck are heave compensated. Seaway causes the coil pipe to slide across the swan neck constantly, thus being bent/straightened out.
The drum is adapted to take up and give out slack in step with the heave compensation, and the coil pipe is, therefore, subjected to many bendings and straightenings due to seaway, reducing the working life of the coil pipe substantially.
A coiled up coil pipe to be passed downwards into the well undergoes three fatigue strains:
--the coil pipe is straightened out when leaving the drum and further on its way towards the swan neck, PA1 --the coil pipe is then curved over the swan neck, and PA1 --the coil pipe is straightened out on its way out from the swan neck, heading for the injector. PA1 --the coil pipe is first curved over the swan neck, PA1 --the coil pipe is straightened on its way out from the swan neck, heading for the drum, and PA1 --the coil pipe is curved upon being coiled up on the drum.
A straightened coil pipe within a well also undergoes three fatigue movements before it is back on the drum:
Thus, a coil pipe which is passed down into the well is totally subjected to at least six fatigue movements before it is back on the drum again. Fatigue movements due to heave compensation of the swan neck should, possibly, be added thereto.
In this connection, it should be mentioned that the method and the device according to the present invention are equally well suited for use in drilling for oil and gas as well as related coil pipe operations both on land and offshore.
Another disadvantage of coil pipe drums and the suspension thereof as well as their positioning consists in that complete drums are expensive, the building up being in part constructively complex, which i.a. is due to the existence of a spooling device for the coil pipe, said spooling device being movable to and fro parallel to drum axis, distributing the coil pipe windings evenly across the length of the hollow core of the drum during coiling operations.
A further disadvantage of known coil pipes undergoing coiling up and uncoiling operations with respect to a rotatable drum is that the course taken by the coil pipe and strains acting thereon may give rise to residual bends in the coil pipe subsequent to straightening. Thus, the coil pipe is not straightened out properly, and it will take a spiral-shaped course within the well. This gives increased friction against the well wall.
There does not exist a known technique to reduce the number of bendings and following straightenings of coil pipes during uncoiling and coiling.